OBD Code B1351: Ignition Key-In Circuit Short To Battery

Q: What does OBD code B1351 mean?

Ignition Key-In Circuit Short To Battery. The ignition key detection circuit is shorted directly to battery voltage, causing the ECU to read an abnormally high signal when the key should be in a specific position. It's like a light switch stuck in the "on" position instead of properly toggling.

Q: What are the symptoms of fault code B1351?

Instrument cluster lights remain on or flicker unexpectedly, Engine may not crank or starts intermittently, Keyless entry or push-button start malfunction

Q: How do I fix OBD fault code B1351?

Inspect the ignition key-in circuit connector for loose, corroded, or pinched wires causing a short to nearby battery supply lines.. Test the ignition switch with a multimeter; if it shows constant high voltage across all positions, replace the switch itself.. Check ECM connectors for corrosion or damaged pins that may be causing the signal line to short internally to power.

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What This Actually Means

In plain language — no jargon

The ignition key detection circuit is shorted directly to battery voltage, causing the ECU to read an abnormally high signal when the key should be in a specific position. It's like a light switch stuck in the "on" position instead of properly toggling.

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Symptoms You May Notice

3 known symptoms for this code

Instrument cluster lights remain on or flicker unexpectedly

Engine may not crank or starts intermittently

Keyless entry or push-button start malfunction

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Embedded Systems Insight

What the ECU/ECM is actually computing

The ECU monitors the ignition key position through a dedicated circuit that should provide variable voltage levels (typically 0-5V) corresponding to key positions like OFF, ACC, RUN, and START. When shorted to battery, this circuit reads full battery voltage regardless of actual key position, confusing the ECU about system state.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
Ignition Key Voltage	0-5V (varies by position)	>4.5V (constant or near-battery)
Circuit Resistance	Variable 0-10kΩ	<100Ω (short to battery)

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Ignition switch wiring harness

Inspect the ignition key-in circuit connector for loose, corroded, or pinched wires causing a short to nearby battery supply lines.

2

Ignition switch assembly

Test the ignition switch with a multimeter; if it shows constant high voltage across all positions, replace the switch itself.

3

Engine control module connectors

Check ECM connectors for corrosion or damaged pins that may be causing the signal line to short internally to power.